mtp: don't create storage device after format data

Since we don't re-create data/media on FBE devices,
don't create an MTP storage device for it.

This fixes the bug when, after formatting data on
and FBE device, an empty Internal Storage appears
on the PC.

This also prevents an empty storage device from
being created if recovery is rebooted after formatting
data before booting to Android. A warning will appear
in the console that MTP is disabled in that case.

Currently the path is hardcoded to data/media; this
should probably be adjusted for cases where adoptable
storage is being used.

Change-Id: Iaafc5e3cde54c3ef6ffaf33f76d14c626b6e590d

partitionmanager.cpp

@@ -2573,6 +2573,12 @@ TWPartition *TWPartitionManager::Get_Default_Storage_Partition()
 
 bool TWPartitionManager::Enable_MTP(void) {
 #ifdef TW_HAS_MTP
+    string mtp_base_path = "/data/media";
+    if (!TWFunc::Path_Exists(mtp_base_path)) {
+		gui_msg(Msg(msg::kWarning, "mtp_base_path_missing=Media storage not found. Unable to enable MTP."));
+		return false;
+	}
+
 	if (mtppid) {
 		gui_err("mtp_already_enabled=MTP already enabled");
 		return true;